This invention relates to semiconductor lasers, and more particularly to distributed Bragg reflector lasers.
Tunable lasers, such as distributed Bragg reflector (DBR) lasers, have applications as light sources in tunable transmitters employed in dense wavelength division multiplex systems. The tuning range may be increased in DBR lasers by increasing the carrier density, and hence decreasing the effective refractive index, in the laser grating section.
DBR lasers with discontinuous tuning can be achieved by having a grating on one side of the laser gain section and a reflecting facet on the other side. The cavity formed therebetween is a Fabry-Perot (FP) etalon and supports FP modes. The Bragg reflectivity spectrum of the grating acts as a tunable-filter which can select an FP mode closest to a Bragg peak at which lasing will occur. Accordingly, as the laser is tuned lasing takes place at discrete FP modes, thereby providing discontinuous tuning. Each of these modes or steps may be aligned to correspond to separate channels in a wavelength division multiplexing system. The number of channels covered by a DBR laser increases as its tuning range increases. Therefore, it is advantageous to maximize the laser tuning range to optimize the number of channels covered.
For a fixed FP cavity length, the lasing frequency is constant within a given tuning step. The lasing frequency, however, may change as tuning current changes within a tuning step. The rate of this undesirable frequency shift with respect to tuning current, df/dI, is called FM efficiency. FM efficiency may be particularly high for DBR lasers as compared to, for example, distributed feedback lasers, making DBR lasers sensitive to RF pick-up and electrical or optical cross-talk. Therefore, there is a need to suppress FM efficiency in DBR lasers to improve RF and noise performance.
A method of fabrication of a distributed Bragg reflector laser is disclosed. The method comprises substantially spatially separated injected carrier electrons from injected carrier holes in a laser waveguide region, thereby reducing bimolecular and Auger recombination rates. Furthermore, material defects are produced in the waveguide region, thereby increasing non-radiative recombination rates of injected carriers.
Further disclosed is a distributed Bragg reflector laser comprising a waveguide region having material defects therein. The laser""s waveguide region has charge carriers comprising electrons and holes which are substantially separated therein.